Lung abscess is a suppurative process characterized by necrosis of lung tissue
Etiology
Common organisms causing lung abscess are
Streptococci
Staphylococcus aureus
Gram negative organisms like Klebsiella pneumoniae
Bacteroides
Fusobacterium
Peptococcus species
Mycobacteria Tuberculosis
mixed organism infection – due to inhalation of foreign material
Pathways by which organisms enter into the lung causing abscess are
Aspiration –
Aspiration of infected material containing anaerobic bacteria from poor oral hygiene, periodontal disease, sinusitis or gingivodental sepsis
other organisms responsible for lung abscess are
Staphylococcus pneumonia
Staphylococcus aureus
Nocardia
Klebsiella pneumoniae
Aspiration occur sin patients of acute alcoholism, coma, anesthesia, debilitation in which cough reflexes are depressed and neurological impairment
Antecedent primary lung infection
Post pneumonia abscess formation associated with S.aureus, K.pneumoniae and type 3 pneumococcus
Spread of infection from infective source
Direct spread of infection from adjacent focus like
subphrenic abscess
Amoebic liver abscess
suppuration in oesophagus
suppurative infection of spine
pericarditis
pleuritis
Trauma – Direct traumatic penetrations (stab wound) into lung
Septic emboli – Septic emboli containing bacteria or fungi reaches lung through circulation. Sources septic emboli are –
Vegetations of infective bacterial endocarditis
Emboli from thrombophlebitis insystemic venous circulation
Neoplasms– neoplasm causes obstruction leading to secondary infection in bronchopulmonary segment causing lung abscess
Hematogenous seedling of lung by pyogenic organisms
If no etiological factor for abscess is identified then it is termed as “primary cryptogenic lung abscess“
Morphology
Gross-
Size – varies in diameter from few mm to 5 to 6cm
Location –
Can affect any part of lung and can be single or multiple
Abscess due to aspiration – commonly in the right lung due to vertical right main bronhcus
Abscess due to pneumonia are multiple and due to bronchiectasis are basal and diffusely scattered
Septic emboli and pyemic abscess – multiple and affect any region of lung
Abscess cavity might be filled with suppurative debris
If there is communication with air passage, then the suppurative material is drained partially and cavity is filled with air.
Continued infection leads to large fetid, green – black, multilocular cavities with poor demarcation of their margins. this is designated as ‘Gangrene of lung’
In chronic cases fibroblastic proliferation produces a fibrous wall
Microscopic appearance
Necrotic material mixed with inflammatory cells surrounded by fibrotic wall. Suppurative area is surrounded by fibrous and granulation trissue
Specific changes may b seen in tubercular abscess (caseous necrosis) or amoebic abscess with extensive dirty white necrosis with trophozoites
Clinical course
Clinical manifestations of lung abscess are
Fever
Cough with Copiouis amount of foul smelling purulent sputum
Chest pain
weight loss
Clubbing of fingers and toes (Few weeks after the onset of abscess)
Radiology helps in confirmation of diagnosis
In older individuals 10 – 15% of cases are associated with carcinomas
Treatment
Antimicrobial therapy – Abscess resolves and leaves scar
If not resolved then leads to further complications
Complications
Lung abscess spreads to other areas causing
Pleuritis and empyema
mediastinitis
meningitis
endocarditis
Osteomyelitis
Systemic amyloidosis
Septicemia
References
Vinay kumar, Abul K.Abbas, Nelson Fausto, Jon C. Aster. Robbins and Cotran Pathologic basis of disease. 9th edition.
AK Mandal, Sharmana Choudhary. Diseases of Respiratory system. In:Text Book of Pathology for MBBS. Volume II. 2012;447-479
Harsh mohan. Text book of Pathology.8th edition.2019
Parakrama Chandrasoma, Clive R. Taylor. The Lung: Structure and Function; Infections. In:Concise pathology. 3rd edition.2001;506-528
